Driver of electric compressor

ABSTRACT

Load fluctuation of a refrigerating cycle under severe conditions needs to be overcome. For instance, a compressor driver which can positively drive the compressor employed even in a vehicle is desirable. To be more specific, at the start of the compressor, a phase of the current flowing in the motor is controlled to be ahead of an induction voltage, then the advancement of the phase is controlled to decrease. Under an unstable condition to detect a position, such as at the start under pressure-difference, the foregoing control allows the phase to advance up to the current-phase where the max. torque can be produced, thereby drawing the instantaneous max. torque of the motor for starting the compressor. Then the control reduces the advancement for obtaining a stable operation. This control method can realize a compressor driver having start-performance enough to overcome pressure-difference.

FIELD OF THE INVENTION

[0001] The present invention relates to drivers of electric compressorsto be used mainly in air-conditioners including a car air-conditioner.

BACKGROUND OF THE INVENTION

[0002] A car air-conditioner including an electric compressor(hereinafter referred to simply as a compressor), which employs asensor-less dc brush-less motor as a driver, is disclosed in, e.g.Japanese Patented Publication No. JP06-156055. This air-conditioner isshown in FIG. 21 which illustrates a schematic structure of thisconventional car air-conditioner including a compressor.

[0003] In FIG. 21, air duct 101 sucks air from air inlet 103 due to anoperation of indoor fan 102, and blows the air undergone indoor heatexchanger 104 into the compartment of the vehicle through air outlet105. Heat exchanger 104 disposed in air-duct 101 forms a refrigeratingcycle together with compressor 106 driven by a sensor-less dc brush-lessmotor, four-way switching valve 107 for selecting heating or cooling byswitching the flow of refrigerant, and outdoor heat exchanger 110 whichexchanges heat of indoor air with that of outdoor air using theoperation of throttle 108 and outdoor fan 109.

[0004] Air-conditioner controller 112 controls the operations ofinverter 111 which operates the sensor-less dc brush-less motor (notshown), i.e. the driver of compressor 106, indoor fan 102, four-wayvalve 107 and outdoor fan 109.

[0005] Air-conditioner controller 112 is connected to various switchessuch as indoor-fan switch 113 for setting ON/OFF, strong/weak of indoorfan 102; air-conditioning switch 114 for selecting cooling, heating orOFF; and temperature-adjustment switch 115. Controller 112 is alsoconnected to communicator 116 for communicating with a vehiclecontroller (not shown). In the foregoing structure, e.g. air-blow isstarted by switch 113, and a weak level of blow is selected, thencooling is instructed by switch 114. Controller 112 sets valve 107 asshown with a solid line in FIG. 21, and works indoor heat exchanger 104as an evaporator and works outdoor heat exchanger 110 as a condenser,and turns on outdoor fan 109, then operates indoor fan 102 on a weaklevel.

[0006] A temperature of indoor heat exchanger 104 is adjusted inaccordance with the setting done by switch 115 taking advantage ofvariable rpm of compressor 106, where the rpm is varied by inverter 111.When cooling/heating is turned off by switch 114, compressor 106 andoutdoor fan 109 are also turned off.

[0007] Turning off of fan switch 113 turns off indoor fan 102, thencompressor 106 and outdoor fan 109 are also turned off for protectingthe refrigerating cycle. On the other hand, an instruction of turningoff the air-conditioner is given from a vehicle controller (not shown)via communicator 116 because of saving power or protecting the battery,controller 112 handles this instruction in the same manner as turningoff the air-conditioner by switch 114.

[0008] When inverter 111 is powered at 120-degree interval drive, themagnetic field changes at. 60-degree intervals (power is fed at60-degree intervals), so that the sensor-less dc brush-less motor (notshown), which drives compressor 106, tends to produce fluctuations intorque.

[0009] A circuit of this power feeding at 120-degree intervals is shownin FIG. 22, where inverter 111 is coupled with battery 121 (powersupply). The dc brush-less motor is operated by inverterswitching-element 122 coupled to battery 121 and the controlling ofinverter diode 123. The dc brush-less motor comprises stator winding 124and magnet rotor 125, and is coupled to battery 121 via inverter 111.

[0010] Inverter 111 comprises the following elements:

[0011] current sensor 126 for detecting a current of the power supplythereby calculating a power consumption and protecting the switchingelements;

[0012] phase shift circuit 127 for detecting a position of magnet rotor125 from a voltage of stator winding 124; and

[0013] phase comparison circuit 128. Control circuit 129 controls ON/OFFof switching element 122 based on signals supplied from sensor 126 andcircuit 128.

[0014] The car air-conditioner including the foregoing compressor issubject to a thermal load environment different from that of a roomair-conditioner. Although a vehicle has a small compartment, it hasrather a large area of window. Since a vehicle runs frequently through asunny place and a shade, it is subject to solar radiation, and thethermal load in the compartment fluctuates frequently. The start/stop ofoperating the compressor depends on switch 114, switch 113, or atemperature adjusting operation set by switch 115, so that thecompressor mounted in a car is frequently started or stopped comparingwith that of a general room air-conditioner.

[0015] Since the compressor mounted in a car is frequently started orstopped, it is required to start or stop before a high pressure side anda low pressure side of the refrigerating cycle are balanced with eachother. In other words, the compressor is started frequently while alarge pressure difference still remains.

[0016] Therefore, the driver of the compressor mounted in a car needsperformance considering every possible operating condition, inparticular, the performance of starting the compressor even if a largepressure difference still remains. This performance is hereinafterreferred to as start-performance under pressure difference.

[0017] To be more specific, the compressor using HFC134a refrigerant isrequired to start even if the difference between a discharge pressureand a suction pressure is as high as 2.0 MPa. This pressure differenceis as much as several times of a driver of a general roomair-conditioner which does not need so often or so much thestart-performance under pressure difference. A method of boostingstart-torque by increasing a voltage (duty ratio) at the start isproposed to a conventional driver of a compressor, e.g. disclosed inJapanese Patent Application Non-Examined Publication No. JP10-47255. Inthis case, a starting current also increases, so that a threshold valuefor current protection also increases.

[0018] However, the methods of increasing only a starting voltage, aduty ratio, or a current threshold value for improving thestart-performance under pressure difference involves increasing thecurrent in a large amount at the same time. Therefore, those methods canstart the compressor under a certain level of pressure difference(according to the experience, the compressor can be started under thepressure difference up to 0.8 MPa). However, when the pressuredifference in the refrigerating cycle exceeds the certain level, theover-current protection is activated, so that the compressor cannotstart.

[0019] The rotor fails in following the rotating magnetic field due tolarge torque loaded, so that the compressor falls in out of sync. at thestart. Once the compressor falls in this state, a positional detectionbecomes unstable, which disables the compressor from starting.

[0020] If the compressor cannot start, the crews and passengers of thevehicle have to wait until the pressure difference in the refrigeratingcycle falls within a range allowing the start. During the waiting time,the temperature of the compartment rises in the condition of coolingoperation, so that the crews and passengers feel uncomfortable. Thevehicle, among others, has a large area of window, so that it is subjectto solar radiation and the thermal load frequently fluctuates in thecompartment. As a result, the crews and passengers feel much moreuncomfortable accordingly.

SUMMARY OF THE INVENTION

[0021] The present invention addresses the problems discussed above, andaims to provide a compressor driver featuring start-performancesufficient to drive the compressor under pressure difference.

[0022] The driver of the present invention has a structure such that itdrives a motor for driving a compressing mechanism which sucks,compresses and discharges fluid. At the start of driving the compressingmechanism, the driver controls such that a current phase of winding ofthe motor advances uniquely from an induction-voltage phase generated atthe winding, then the advancement of the winding current-phasedecreases.

[0023] Under an unstable condition in which a large pressure differencetends to remain, the foregoing structure allows the current phase toadvance uniquely to a certain level, where starting torque sufficient tostart the compressing mechanism under a pressure difference can begenerated. Then the motor produces the sufficient torque to start thecompressing mechanism. In order to deal with unstable fluctuation of thetorque, the advancement of the current phase is reduced, so that thecompressing mechanism operates in a stable manner. As a result, thedriver can exert its start-performance under pressure difference, andthe compressor can be positively started.

[0024] The compressor driver of the present invention can decrease theadvancement of the winding current-phase in either one of the followingcases: (a) a lapse of a given time; (b) an rpm of the motor reaches agiven rpm. This structure allows decreasing the current phase afterstarting the compressor, thereby controlling the compressor not to fallinto an unstable operation. As a result, the compressor can stay in astable operation.

[0025] The compressor driver of the present invention can draw themaximum instantaneous torque from the motor depending on an advancementof the winding current-phase. This structure allows starting thecompressor such that the maximum instantaneous torque can be uniquelyproduced by the motor, so that the compressor can be positively startedeven if a large pressure difference in the refrigerating cycle stillremains.

[0026] The compressor driver of the present invention switches a dcvoltage supplied from a dc power supply, thereby outputting an ac(alternating current) in sine waveform to the sensor-less dc brush-lessmotor. Detection of a current running through the stator winding allowsdetermining a position of the rotor having permanent magnets of thesensor-less dc brush-less motor, so that the switching of the dc voltagecan be controlled. This structure allows each carrier to detect aposition of the rotor and to adjust an output, so that thestart-performance can be further improved.

[0027] The compressor driver of the present invention carries outswitching with three-phase modulation. This structure makes a carrierfrequency be equivalent to doubled, so that a smooth current can beexpected. As a result, smaller torque fluctuation is produced and thestart-performance can be improved.

[0028] The compressor driver of the present invention is mountable to acar air-conditioner. This structure ensures to drive the compressorpositively in a vehicle which is subject to a severe condition includingload fluctuation of the refrigerating cycle. As a result, the driverimproves the performance and function of the car air-conditioner.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 shows a schematic circuit diagram of a compressor driver inaccordance with an exemplary embodiment of the present invention.

[0030]FIG. 2 illustrates a relation between phase-current i_(u) andinduction voltage Eu of phase-U in a compressor driver in accordancewith an exemplary embodiment of the present invention.

[0031]FIG. 3 shows waveforms of a voltage and a waveform of current byone-phase of a sensor-less dc brush-less motor in accordance with anexemplary embodiment of the present invention.

[0032]FIG. 4 depicts waveforms showing modulations in respective phasesat the maximum modulation 100% of three-phase modulation in accordancewith an exemplary embodiment of the present invention.

[0033]FIG. 5 depicts waveforms showing modulations in respective phasesat the maximum modulation 50% of three-phase modulation in accordancewith an exemplary embodiment of the present invention.

[0034]FIG. 6 depicts waveforms showing modulations in respective phasesat the maximum modulation 10% of three-phase modulation in accordancewith an exemplary embodiment of the present invention.

[0035]FIG. 7 shows a timing chart illustrating a method of detecting aphase current in accordance with an exemplary embodiment of the presentinvention.

[0036]FIG. 8 shows a circuit diagram illustrating a current path inpower-feed timing (a) shown in FIG. 7.

[0037]FIG. 9 shows a circuit diagram illustrating a current path inpower-feed timing (b) shown in FIG. 7.

[0038]FIG. 10 shows a circuit diagram illustrating a current path inpower-feed timing (c) shown in FIG. 7.

[0039]FIG. 11 shows a circuit diagram illustrating a current path inpower-feed timing (d) shown in FIG. 7.

[0040]FIG. 12 shows a structure of a magnet rotor of an IPM motor inaccordance with an exemplary embodiment of the present invention.

[0041]FIG. 13 shows characteristics of current-phase and torque at startup mode in accordance with an exemplary embodiment of the presentinvention.

[0042]FIG. 14 shows characteristics of current-phase and torque atsteady low speed mode in accordance with an exemplary embodiment of thepresent invention.

[0043]FIG. 15 shows characteristics of current-phase and torque atsteady medium speed mode and at steady high speed mode in accordancewith an exemplary embodiment of the present invention.

[0044]FIG. 16 illustrates a relation between current phase and time inaccordance with an exemplary embodiment of the present invention.

[0045]FIG. 17 illustrates a relation between current phase and rpm ofthe motor in accordance with an exemplary embodiment of the presentinvention.

[0046]FIG. 18 shows a flowchart illustrating a control (selecting acondition of reducing a current phase) including respective operationmodes in accordance with an exemplary embodiment of the presentinvention.

[0047]FIG. 19 shows a schematic circuit diagram of another compressordriver in accordance with an exemplary embodiment of the presentinvention.

[0048]FIG. 20 shows a sectional view of a compressor employing thecompressor driver in accordance with an exemplary embodiment of thepresent invention.

[0049]FIG. 21 shows a structure of a car air-conditioner employing aconventional compressor.

[0050]FIG. 22 shows a circuit diagram of driving at 120-degree intervalsof a car air-conditioner employing a conventional compressor.

DETAILED DESCRIPTION OF THE INVENTION Best Mode for Carrying out theInvention

[0051] A driver of a compressor mounted in a car air-conditioner inaccordance with an exemplary embodiment of the present invention isdemonstrated hereinafter with reference to the accompanying drawings.

Exemplary Embodiment

[0052] An electric circuit in accordance with the exemplary embodimentof the present invention is described with reference to FIG. 1, whichshows a schematic circuit diagram of the compressor driver in accordancewith the embodiment of the present invention.

[0053] In FIG. 1, inverter 20 is coupled with battery 1, i.e. a powersupply, and sensor-less brush-less motor M (hereinafter referred tosimply as a motor). Inverter 20 comprises the following elements:

[0054] inverter module I;

[0055] current sensor 6 for detecting a current necessary to drive motorM; and

[0056] control circuit 7 for controlling switching elements 2 based onsignals supplied from current sensor 6.

[0057] Inverter Module I Includes the Following Elements:

[0058] plural switching elements 2 for operating the inverter, elements2 being coupled to battery 1; and

[0059] diodes 3 for operating the inverter.

[0060] Switching Elements 2 Comprises the Following Elements:

[0061] upper switching elements U, V, W;

[0062] lower switching elements X, Y, Z; and

[0063] diodes 3U, 3V, 3W, 3X, 3Y, and 3Z, respectively coupled betweenthe source and drain of each one of the upper and lower switchingelements. Motor M comprises stator winding 4 and magnet rotor 5.

[0064] The circuit of the compressor driver of the present inventionshown in FIG. 1 is compared with the circuit in FIG. 22 for driving theconventional compressor at 120-degree intervals. The comparison tellsthat the circuit shown in FIG. 1 eliminates phase comparing circuit 128and phase-shift circuit 127.

[0065] In FIG. 1, a current value detected by sensor 6 is sent tocontrol circuit 7, and used for calculating a power consumption orprotecting switching elements 2, and the current value detected is alsoused for detecting a position of magnet rotor 5 of motor M. Controlcircuit 7 controls the power-feeding to switching elements 2 based on anrpm instruction signal (not shown) in order to carry out a temperatureadjustment set by temperature-adjustment switch 115 shown in FIG. 21,which shows a schematic structure of a conventional car air-conditioner.Meanwhile, current sensor 6 can be anything like a sensor using a Hallelement or a shunt resistor, which can detect a peak value of theswitching current produced by switching elements 2. In FIG. 1, sensor 6is disposed at the minus side of the power line; however, since thecurrent is the same, it can be disposed at the plus side.

[0066] The foregoing structure allows eliminating comparing circuit 128and phase-shift circuit 127 from the conventional compressor driver, sothat the driver of the present invention can be not only downsized andreduced the weight, but also improved reliability such as obtainingbetter vibration proof.

[0067] Next, a method of detecting a position of magnet rotor 5 of motorM shown in FIG. 1 is demonstrated hereinafter. FIG. 2 illustrates arelation between phase-current i_(u) and induction voltage E_(u) ofphase-U in the compressor driver in accordance with the embodiment ofthe present invention. Induction voltage E_(u) is induced at statorwinding 4 by the rotation of magnet rotor 5 shown in FIG. 1, so that theposition of rotor 5 can be determined by monitoring a signal of theinduction voltage.

[0068] In FIG. 1, stator winding 4 has inductance L and resistance R asshown in FIG. 2. The sum of induction voltage E_(u), a voltage inducedat inductance L, and a voltage across resistor R equals to a voltageapplied by inverter 20. The voltage across resistor R is expressed asR·i_(u) (iu=phase current), and the voltage induced across inductance Lis expressed as L·di_(u)/dt, so that the voltage (Vu) applied byinverter 20 is expressed as follows:

[0069] Vu=E_(u)+R·i_(u)+L·di/dt thus the induction voltage Eu can beexpressed as E_(u)=V_(u)−R·i_(u)−L·di_(u)/dt

[0070] Control circuit 7 shown in FIG. 1 controls switching elements 2,and a value of applied voltage Vu is known. Thus pre-set of the valuesof inductance L and resistor R in the program software, i.e. acalculating means installed in control circuit 7, will calculateinduction voltage E_(u) only by detecting phase-U current i_(u). FIG. 3shows voltages and a waveform of current by one phase of motor M.

[0071] Next, a method of detecting a position of magnet rotor 5 withcurrent sensor 6 is demonstrated hereinafter. FIG. 4 through FIG. 6 showrespective waveforms of three-phase modulation with phase-U terminalvoltage 41, phase-V terminal voltage 42, phase-W terminal voltage 43 andneutral-point voltage 29. FIG. 4 shows the maximum modulation 100%, FIG.5 shows the maximum modulation 50%, and FIG. 6 shows the maximummodulation 10%.

[0072] Detection of current by sensor 6 is detailed here. FIG. 7 shows atiming of power-feeding within one carrier (carrier cycle) to upperswitching elements U, V, W and lower switching elements X, Y, Z. In thiscase, the maximum modulation of 50% shown in FIG. 5 is powered atapprox. 130-degree. Because of the three-phase modulation, patterns (a),(b), (c) and (d) as shown in FIG. 7 are set as feeding patterns.

[0073]FIG. 8 shows a current flow in feeding pattern (a), i.e. upperswitching elements U, V, W are all OFF, and lower switching elements X,Y, Z are all ON. In this case, phase-U current i_(u) and phase-V currentiv flow respectively from diodes 3X, 3Y disposed in parallel with lowerswitching elements X, Y to stator winding 4. Phase-W current w flowsfrom stator winding 4 to lower switching element Z, so that the currentcirculates within this route. As a result., no current flows throughsensor 6, so that no current is detected.

[0074] Next, in the case of feeding pattern (b) moved from pattern (a),the current-flow is shown in FIG. 9, i.e. upper switching element U isON, and lower switching element Y, Z are ON. In feeding pattern (b),phase-U current i_(u) flows from element U to stator winding 4, phase-Vcurrent iv flows from diode 3Y disposed in parallel with element Y tostator winding 4, and phase-W current i_(w) flows from stator winding 4to element Z. Thus phase-U current i_(u) flows through sensor 6, so thatthe current value is detected.

[0075] In the case of feeding pattern (c) moved from pattern (b), thecurrent-flow is shown in FIG. 10; i.e. upper switching elements U, V areON, and lower switching element Z is ON. In feeding pattern (c), phase-Ucurrent iu and phase-V current iv flow respectively from elements U, Vto stator winding 4, and phase-W current i_(w) flows from stator winding4 to element Z. Thus phase-W current i_(w) flows through sensor 6, sothat the current value is detected.

[0076] In the case of feeding pattern (d) moved from pattern (c), thecurrent-flow is shown in FIG. 11, i.e. upper switching elements U, V, Ware all ON, and lower switching elements X, Y, Z are all OFF. In feedingpattern (d), phase-U current i_(u) and phase-V current iv flowrespectively from elements U, V to stator winding 4, and phase-W currentiw flows from stator winding 4 to diode 3W disposed in parallel withelement W. The current circulates in this route. Thus no current flowsthrough sensor 6, so that no current is detected.

[0077] As discussed above, phase-U current i_(u) and phase-W currenti_(w) are detected by current sensor 6, so that remaining phase-Vcurrent iv can be found using Kirchhoff's law at the neutral point onstator winding 4. In this case, phase-U current i_(u) flows into theneutral point on stator winding 4, and phase-W current i_(w) flows outfrom the neutral point of stator winding 4. Thus phase-V current iv canbe found from the difference between iu and iw.

[0078] The current detection discussed above can be carried out at eachone of carriers, so that a position can be detected at each carrier andan output to stator winding 4 can be adjusted. Therefore, the compressordriver of the present invention, which uses the method of detecting aposition of the magnet rotor with the current sensor, has smaller torquefluctuations and better start-performance than those of the conventionalone which uses 120-degree intervals for power-feeding.

[0079] Further, in the three-phase modulation, as discussed above, sincethe current circulates in inverter module I and stator winding 4 duringfeeding patterns (a) and (d) within a carrier cycle, the power current(the current flowing through sensor 6) dose not flow. Thus the power isfed twice, i.e. in the first half and the latter half of a carriercycle. It is equal to doubling the carrier frequency, and the currentfluctuation becomes smooth. In other words, the three-phase modulationproduces smaller torque fluctuations and better start-performance than atwo-phase modulation.

[0080] Next, the torque for driving magnet rotor 5 is describedhereinafter. FIG. 12 shows magnet rotor 5 of IPM (interior permanentmagnet) motor in which magnets are buried in magnet rotor 5. Rotor 5comprises permanent magnets 10 and magnet rotor-cores 11. Since the IPMmotor has interior permanent magnets 10 in rotor 5, an inductance viewedfrom the stator winding varies depending on a position of rotor 5. To bemore specific, there are two positions, one is a position (direction “d”in FIG. 12) where the inductance is blocked by a magnet having a largemagnetic reluctance to flow through a magnetic path, and the other oneis a position (direction “q”) where the inductance flows through siliconsteel plate having a small magnetic reluctance. This difference in theinductance produces reluctance torque.

[0081]FIG. 13 shows a relation of the torque given off by the IPM motorto phase difference β (current-phase) between the induction voltage andthe phase current of stator winding 4 of the IPM motor. In FIG. 13, whenthe current phase stays in the plus region (right hand side of β=0 inFIG. 13), rotor 5 (induction voltage) is behind the current. On theother hand, when the current phase stays in the minus region (left handside of β=0 degree in FIG. 13), rotor 5 (induction voltage) is ahead ofthe current. The magnet torque reaches its maximum at β=0 degree, andthe reluctance torque reaches 0 (zero) at β=0 degree, reaches itsmaximum at β=45 degrees, and reaches a maximum on the minus side atβ=−45 degrees. In the case shown in FIG. 13, the total torque of themagnet torque and the reluctance torque reaches the maximum at the pointshifted toward the right by approx. 20 degrees.

[0082] In general, magnet torque is proportionate to current, andreluctance torque is proportionate to current squared. The instanceshown in FIG. 13 takes place in a start-up mode, where a current notless than 20 A often flows as a starting current, namely, a largecurrent flows in starting. In this case, the total torque reaches themaximum at β=20 degrees.

[0083] As a result, the switching of the inverter is preferablycontrolled to achieve β=20 degrees in order to improve thestart-performance under pressure difference in the start-up mode. Thiscontrol mode is referred to as a start-up mode.

[0084] In this embodiment, a maximum point for giving off the maximumtorque is selected so that the driver can start positively under thepressure difference. However, instead of this selection, a phase can beadvanced uniquely to a current phase (e.g. β=18 degrees in FIG. 13)where starting torque can be produced enough for the start under thepressure difference. In the instance shown in FIG. 13, the phase can beset within the range which does not exceed 20 degrees, i.e. the maximumtorque. This is preferable for stable operation of the motor and forsaving power.

[0085] Table 1 lists experimental data showing a relation betweencurrent-phase at the starting and a pressure difference allowable forthe starting. The experiment tells that the pressure difference allowingthe start reaches the maximum at current-phase β=20 degrees. At β=10degrees and β=30 degrees, the pressure difference reaches the same valueallowing the start. Those results are in accordance with thecharacteristics shown in FIG. 13. TABLE 1 experimental data showingrelations between current-phase and pressure difference allowing thestart Pressure difference allowing the start (just Phase-current beforethe compressor at the start is turned off) Remarks  0 degree 1.5 MPa  5degrees 1.7 MPa 10 degrees 2.0 MPa 15 degrees 2.2 MPa 20 degrees 2.3 MPaPhase set at the start 30 degrees 2.0 MPa

[0086]FIG. 14 shows relations between phase-difference β (current-phase)and the torque directly after the start. Directly after the start, thecurrent lowers to approx. 15 A, so that magnet torque and reluctancetorque also lower. Since the reluctance torque in particular isproportionate to the current squared, it lowers so great that themaximum point of the total torque shifts to the left. In the instanceshown here, the maximum point shifts to the point of β=17 degrees.

[0087] As a result, it can be considered that the switching of theinverter is controlled to be at β=17 degrees directly after the start;however, this control simply results in lowering the torque because ofthe following reasons, and as a result, rotor 5 delays in rotation, andeventually, rotor 5 stops rotating.

[0088] The reason is this: in general, directly after the start, the rpmdoes not reach a high enough level yet, so that the motor is still inunstable rotating status. The refrigerating cycle has also restartedfrom the state in which a large pressure difference between thehigh-pressure side and the low-pressure side remained. Thus thecondenser's fan has restarted and the condensing operation still remainsin unstable status. In such a condition, when the switching of inverter20 is controlled such that β=17 degrees is achieved immediately afterthe start, a delay in rotating of rotor 5 due to torque fluctuation(causing larger current-phase β) will lower the torque.

[0089] Therefore, immediately after the start, the switching of theinverter is preferably controlled such that the compressor can beoperated steadily. For this purpose, in this embodiment, the switchingof inverter 20 is controlled at the current-phase enough away to theleft from the maximum point of the total torque. To be more specific, asmall enough current-phase such as β=5 degrees is used as shown in FIG.14, so that a delay in rotating of rotor 5 due to torque fluctuation(causing a larger current-phase β) will increase the torque, and thedelay of rotor 5 can be cancelled. If rotor 5 is ahead of current(corresponding to a smaller current-phase β), the torque decreases andthe advancement of rotor 5 can be cancelled. As a result, the motor iscontrolled to rotate steadily, in particular, immediately after thestart, so that the compressor can start in a stable manner. This controlmode is referred to as a steady low-speed mode.

[0090]FIG. 15 shows relations between phase-difference β (current-phase)and the torque during steady rotation of the motor. During this steadyperiod, the current decreases in general to approx. 10 A. The magnettorque as well as the reluctance torque also decreases; however, sincethe reluctance torque decreases much greater, the maximum point of thetotal torque shifts to the left in FIG. 15. In the instance shown inFIG. 15, the torque reaches the maximum value at phase-current β=13degrees. Based on the foregoing discussion, in the region where thetotal torque fluctuates only a little and yet the total torquesufficient for the driving is reserved, the switching of inverter 20 iscontrolled, considering the motor current, such that current-phase β=10degrees is achieved. This control mode is referred to as a steady mediumspeed mode.

[0091] In the case of using a field weakening for obtaining a greaterrpm, the switching of inverter 20 is controlled such that current-phaseβ further increases (max. 30 degrees). This control obtains the totaltorque on the right side from the maximum point of β=13 degrees, and thetotal torque obtained becomes almost flat, and yet, both of the rpm andthe refrigerating cycle of the motor become stable, so that a stableoperation can be expected. This control mode is referred to as a steadyhigh-speed mode.

[0092]FIG. 16 shows a timing chart illustrating relations betweenphase-difference β (current-phase) and time in the start-up mode, steadylow-speed mode, and steady medium-speed mode. In the instance shown inFIG. 16, the start-up mode lasts 6 seconds from the start and β=20degrees is uniquely kept. Then the current-phase moves on to β=5 degreesin the steady low-speed mode, and the current-phase moves on to β=10degrees in the steady medium-speed mode.

[0093]FIG. 17 shows an output content of a control signal, where thecontent illustrates relations between phase difference β and the rpm ofthe motor in the start-up mode, steady low-speed mode, steadymedium-speed mode, and steady high-speed mode.

[0094] In the instance shown in FIG. 17, the motor operates in thestart-up mode with β=20 degrees until the motor reaches 900 rpm or lapseof 6 seconds after the start, whichever the faster one. Then the motoroperates in the steady low-speed mode with β=5 degrees until the motorreaches 1200 rpm, next, the motor operates in the steady medium-speedmode with β=10 degrees until 7200 rpm. Further, the current-phasebecomes greater up to β=30 degrees in the steady high-speed mode and themotor is controlled to reach max. 9000 rpm.

[0095]FIG. 18 shows a flowchart illustrating the control including theforegoing operation modes. At the start, the compressor driver is set inthe start-up mode, and the timer starts (step S10). In step 10,current-phase β is set at 20 degrees, and carrier frequency is set at4.3 kHz before the operation starts. The reason why the carrierfrequency is set at rather a low level is that a lower rpm willpositively obtain resolving power, and a time for feeding power withinone carrier is obtained so that the current can be detected with ease.The low carrier frequency also produces the following benefits: the timefor feeding power within one carrier can be adjusted correctly withease, and phase-current β can be controlled with ease, and greatertorque is obtainable with accuracy.

[0096] Next, it is determined whether or not the timer counts 6 seconds,or whether or not the actual rpm reaches 900 rpm (step S20). If thedetermination in step S20 is “No”, this item is determined again, and ifthe determination is “Yes”, the control moves on to step S30.

[0097] Next, it is determined whether or not an actual rpm is less than1200 rpm (step S30). If “Yes”, the control moves on to step S40. If“No”, the control moves on to step S45.

[0098] In step S40, the motor is set in the steady low-speed mode, andthe current-phase is set at β=5 degrees, the carrier frequency is set at4.3 kHz. The reason why the carrier frequency is set at rather a lowlevel is already described in step S10. This setting allows controllingthe current-phase with ease and preventing the motor from abnormaloperation.

[0099] On the other hand, in step S45, it is determined whether or notan actual rpm is less than 7200 rpm. If the determination is “Yes”, thecontrol moves on to step S50. If “No”, the control moves on to step S55.In step S50, the motor is set in the steady medium-speed mode, and thecurrent-phase is set at β=10 degrees, the carrier frequency is set at7.5 kHz. In step S55, the motor is set in the steady high-speed mode,and the current-phase is set at β=10 degrees plus a value proportionateto the rpm {f (rpm)} because of the field weakening, the carrierfrequency is set at 7.5 kHz.

[0100] Then the control moves back to step S30, and repeats the controlfollowing the flowchart shown in FIG. 18.

[0101] If motor M is halted due to the temperature adjustment or thelike, and motor M needs to restart, the control is carried out followingthe foregoing flowchart from step S10. In other words, independent ofON/OFF of operating the air-conditioner, each one of starts of thecompressor at intermittent operations involved in adjusting atemperature can be controlled in a similar manner to what is discussedabove.

[0102] In the foregoing embodiment, an IPM motor is used; however, anSPM (surface permanent magnet) motor can be used with a similaradvantage. Not only when a motor starts, but also when a refrigeratingcycle falls in a transient state, a delay of current-phase β in advanceallows the motor to operate in a stable manner. This embodiment isapplicable not only to the refrigerating cycle but also to high-torquestart of a motor. This embodiment is also applicable to driving acompressor coupled to a motor on a belt. In this embodiment, thethree-phase modulation is taken for example; however, the control methodof this embodiment is applicable to a two-phase modulation.

[0103]FIG. 19 shows another circuit in accordance with the exemplaryembodiment of the present invention. In FIG. 19, two current sensor areadded to the circuit shown in FIG. 1, namely, current sensor 8 fordetecting a current of phase-U of inverter 21 and current sensor 9 forphase-W. Other points remain unchanged from the circuit shown in FIG. 1,so that the elements in FIG. 19 have the same reference marks as thosein FIG. 1, and the descriptions thereof are omitted here.

[0104] In the foregoing another circuit, sensors 8, 9 detectrespectively the phase-currents of phase-U and phase-V The current ofthe remaining one-phase can be found by the same method alreadydescribed in the embodiment. The control of obtaining the max. torque orany torque at the start under pressure-difference can be done in thesame manner already demonstrated in the embodiment, so that thedescription about this control is omitted here.

[0105]FIG. 20 shows a structure where inverter 20 is mounted solidly tothe left-side end of airtight compressor 40. Air-tight compressor 40 hasa known structure where metal enclosure 32 houses compressing mechanism28, motor 31. Refrigerant is sucked through inlet 33 and compressed bycompressing mechanism 28 driven by motor 31. (In FIG. 20, a scrollcompressing mechanism is employed.) The compressed refrigerant passesthrough motor 31 (for cooling the motor), and is discharged from outlet34. Terminal 39 internally coupled to the winding of motor 31 isconnected to inverter 20.

[0106] Inverter 20 is accommodated in housing 30 which is mounted tocompressor 40. Inverter circuit 37, i.e. a heat source, is mounted tohousing 30 so that the heat can travel through housing 30 to metalenclosure 32 of compressor 40. In other words, inverter circuit 37 iscooled by the refrigerant in compressor 40 via metal enclosure 32.

[0107] Terminal 39 is coupled to an output section of inverter circuit37. Connecting wire 36 includes power-wire 36 a coupled to battery 1 andcontrolling signal wire 36 b coupled to the air-conditioner controller(not shown). Motor 31 employs the concentrated winding instead of thedistributed winding because a shorter lateral length is obtainable. Theconcentrated winding produces greater inductance, so that it takes alonger feed-back time to the diode, thus the concentrated winding makesthe position detection difficult, and the control of the positiondetection becomes also difficult. However, in the case of driving insine-waveform, a position is detected with a current, so that thedetection is controllable.

[0108] The compressor incorporating the inverter as discussed aboveneeds smaller inverter 20 and vibration proof. For reducing vibration,it is preferable to use the three-phase modulation, which smoothes acurrent in sine-waveform and reduces vibration, so that the three-phasemodulation is suitable for the compressor driver in accordance with theembodiment of the present invention.

[0109] A battery is used as a dc power supply of the compressor driverin this embodiment; however a commercial power can be rectified into dcto be used as the power supply instead of the battery. Any power as longas it is rectified into dc can be used in a home-use compressor driveror other compressor drivers.

[0110] The compressor driver of the present invention is controlled suchthat a phase advancement with respect to an induction voltage of thecurrent which flows in the motor is temporarily increased at the startof the compressor, and then reduced. Therefore, even in an unstablestatus for detecting the rotor position at the start, the phase isadvanced up to the current-phase where torque sufficient to startdriving under pressure-difference is obtainable, and instantaneoustorque of the motor is given off to drive the compressor. Then thecurrent-phase is delayed in order to realize a stable operation. As aresult, the start-performance under pressure difference is positivelycarried out, and unstable torque fluctuation can be dealt with.Therefore, this compressor driver can positively drive the compressoreven if it is employed, e.g. in a vehicle which must bear the loadfluctuation of the refrigerating cycle under sever conditions. Thus thecompressor driver of the present invention is suitable for a carair-conditioner.

Description of Reference Marks

[0111]1 battery

[0112]2 switching element

[0113]3 diode

[0114]4 stator winding

[0115]5 magnet rotor

[0116]6 current sensor

[0117]7 control circuit

[0118]8 current sensor for phase-U

[0119]9 current sensor for phase-W

[0120]20 inverter

[0121]21 inverter including a current sensor which detects a phasecurrent

[0122]30 housing

[0123]31 motor

[0124]40 compressor

1. A driver of an electric compressor for driving amotor which drives acompressing mechanism that sucks fluid, then compresses and dischargesthe fluid, wherein the driver controls such that a current-phase ofwinding of the motor is advanced uniquely with respect to an inductionvoltage-phase generated in the winding at start of driving thecompressor, then the advancement of the current-phase is reduced.
 2. Thedriver of claim 1 controls such that the advancement of thecurrent-phase is reduced at one of when a given time passes and when themotor reaches a given rpm.
 3. The driver of claim 1 draws instantaneousmaximum torque of the motor depending on the advancement of thecurrent-phase of the winding.
 4. The driver of claim 1 switches a dcvoltage supplied from a dc power supply for outputting an ac insine-waveform to a sensor-less dc brush-less motor, and detects acurrent flowing through a stator winding for determining a position of arotor, having a permanent magnet, of the sensor-less dc brush-lessmotor, so that the switching of the dc voltage is controlled.
 5. Thedriver of claim 4, wherein the switching is done in three-phasemodulation.
 6. The driver of claim 1, wherein the driver is mounted to acar air-conditioner.
 7. The driver of claim 2, wherein the driver ismounted to a car air-conditioner.
 8. The driver of claim 3, wherein thedriver is mounted to a car air-conditioner.
 9. The driver of claim 4,wherein the driver is mounted to a car air-conditioner.
 10. The driverof claim 5, wherein the driver is mounted to a car air-conditioner.